Chalk Bluff Staging Area
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chalk Bluff Staging Area clear sky chart from 2005-11-06 to 2025-12-18.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	9% 6% 1 3 2 2 2 2 3 4 64%	135827
	Night	11% 7% 1 3 2 2 3 2 4 5% 59%	132607
Transparency	Day	26% 2 6% 18% 26% 22%	130773
	Night	30% 3 6% 17% 23% 20%	128645
Seeing	Day	17% 15% 32% 24% 9% 3	16513
	Night	16% 8% 21% 32% 20% 4	25848

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	16% 13% 2 4 3 2 3 3 4 6% 44%	3639
	11th to 20th	Day	15% 9% 2 4 3 3 2 2 3 3 55%	3870
	21st to end	Day	18% 9% 2 4 3 2 2 2 3 5% 49%	4510
February	1st to 10th	Day	21% 11% 2 3 2 2 3 2 4 6% 44%	1800
	11th to 20th	Day	16% 14% 2 4 3 3 3 2 5% 6% 42%	1893
	21st to end	Day	17% 16% 2 4 2 2 2 2 4 4 44%	1650
March	1st to 10th	Day	17% 23% 4 5% 3 3 3 2 4 5% 30%	4595
	11th to 20th	Day	16% 16% 2 3 2 2 2 2 3 4 47%	5000
	21st to end	Day	20% 20% 2 4 3 3 3 3 4 5% 33%	5743
April	1st to 10th	Day	16% 12% 2 4 3 3 4 3 4 6% 42%	2400
	11th to 20th	Day	14% 8% 2 4 3 3 3 3 4 5% 51%	2369
	21st to end	Day	12% 7% 1 4 3 3 3 2 5% 6% 55%	2400
May	1st to 10th	Day	6% 5% 1 3 2 2 2 2 3 5% 70%	5650
	11th to 20th	Day	7% 3 1 3 2 2 2 2 3 4 71%	6277
	21st to end	Day	5% 2 1 2 2 2 2 2 3 5% 76%	6902
June	1st to 10th	Day	8% 5% 1 4 3 3 3 3 5% 6% 60%	2800
	11th to 20th	Day	4 2 2 1 2 2 2 4 5% 76%	2800
	21st to end	Day	3 1 1 2 2 1 1 2 2 2 83%	2800
July	1st to 10th	Day	1 1 1 1 1 2 93%	6319
	11th to 20th	Day	1 1 1 1 1 1 1 2 2 89%	6320
	21st to end	Day	1 1 1 2 2 2 2 2 3 3 82%	6563
August	1st to 10th	Day	2 1 1 2 1 1 2 2 2 3 84%	5777
	11th to 20th	Day	1 1 1 1 1 1 1 2 91%	5415
	21st to end	Day	2 1 1 2 1 2 2 2 2 3 82%	5984
September	1st to 10th	Day	2 1 1 1 1 2 1 2 3 85%	2400
	11th to 20th	Day	5% 2 1 3 2 2 2 2 4 5% 73%	2400
	21st to end	Day	5% 3 1 2 2 1 2 1 3 4 76%	2170
October	1st to 10th	Day	5% 3 1 3 2 2 2 3 4 5% 71%	3280
	11th to 20th	Day	9% 2 1 2 2 2 2 2 3 5% 69%	3261
	21st to end	Day	7% 4 1 4 3 3 4 3 4 6% 60%	3558
November	1st to 10th	Day	13% 8% 2 3 3 3 3 3 4 6% 53%	1855
	11th to 20th	Day	16% 5% 1 4 4 3 4 3 6% 6% 48%	1890
	21st to end	Day	12% 9% 1 4 3 3 3 3 4 5% 53%	1749
December	1st to 10th	Day	11% 4 1 3 3 3 3 4 5% 6% 58%	2700
	11th to 20th	Day	27% 11% 2 4 3 3 3 3 5% 6% 33%	3084
	21st to end	Day	24% 9% 2 5% 3 4 4 3 6% 7% 33%	4004
January	1st to 10th	Night	12% 12% 3 4 3 3 4 4 5% 7% 43%	6306
	11th to 20th	Night	16% 7% 2 3 3 3 3 2 3 5% 53%	6083
	21st to end	Night	15% 11% 2 5% 3 4 3 2 4 5% 46%	6468
February	1st to 10th	Night	19% 8% 3 4 3 2 3 2 4 6% 46%	2600
	11th to 20th	Night	14% 12% 2 4 3 4 4 3 5% 5% 43%	2392
	21st to end	Night	16% 12% 3 5% 2 2 3 2 3 6% 46%	1980
March	1st to 10th	Night	18% 20% 4 4 3 3 3 2 3 6% 34%	5296
	11th to 20th	Night	19% 17% 2 3 2 2 2 2 2 4 46%	5000
	21st to end	Night	19% 19% 2 4 3 3 3 3 4 6% 33%	5231
April	1st to 10th	Night	14% 12% 2 4 3 3 3 3 6% 5% 46%	2000
	11th to 20th	Night	13% 9% 2 3 3 2 4 2 5% 6% 52%	1979
	21st to end	Night	10% 6% 1 3 2 2 3 3 4 6% 59%	2000
May	1st to 10th	Night	4 5% 1 3 2 2 3 2 4 4 69%	4337
	11th to 20th	Night	4 3 1 3 3 2 2 3 4 4 71%	3616
	21st to end	Night	4 2 1 2 1 2 2 2 2 4 77%	3972
June	1st to 10th	Night	8% 5% 1 2 2 2 2 3 5% 6% 64%	1600
	11th to 20th	Night	3 2 2 2 1 2 2 4 5% 78%	1600
	21st to end	Night	3 2 1 2 2 1 2 1 3 4 80%	1600
July	1st to 10th	Night	1 1 1 1 1 2 92%	3640
	11th to 20th	Night	2 1 1 2 1 1 1 1 2 2 86%	3640
	21st to end	Night	2 1 1 2 2 2 2 2 4 4 78%	4286
August	1st to 10th	Night	2 2 1 2 1 1 2 2 3 4 80%	4035
	11th to 20th	Night	1 1 1 1 1 1 2 3 90%	4450
	21st to end	Night	3 2 1 2 1 2 2 2 2 3 81%	5015
September	1st to 10th	Night	2 1 1 1 1 1 2 2 4 84%	2000
	11th to 20th	Night	4 2 1 3 2 2 2 2 3 4 76%	2000
	21st to end	Night	3 2 1 2 1 2 2 2 4 5% 76%	2225
October	1st to 10th	Night	4 3 1 3 2 2 2 1 2 3 77%	3920
	11th to 20th	Night	5% 2 1 2 2 2 2 1 3 4 76%	3897
	21st to end	Night	11% 3 1 2 2 2 3 3 5% 5% 63%	4253
November	1st to 10th	Night	15% 7% 2 3 2 2 3 3 4 7% 54%	2663
	11th to 20th	Night	13% 6% 2 4 3 3 3 3 5% 7% 51%	2730
	21st to end	Night	12% 8% 1 4 3 3 3 3 4 6% 55%	2867
December	1st to 10th	Night	11% 4 1 2 2 3 3 3 3 6% 62%	4700
	11th to 20th	Night	25% 12% 2 4 2 3 4 3 6% 8% 30%	5274
	21st to end	Night	27% 12% 2 5% 3 4 4 3 4 5% 31%	6952

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	43% 4 11% 18% 15% 9%	3639
	11th to 20th	Day	38% 2 6% 15% 23% 16%	3870
	21st to end	Day	41% 3 6% 14% 20% 18%	4510
February	1st to 10th	Day	43% 3 9% 16% 19% 11%	1800
	11th to 20th	Day	44% 3 8% 18% 20% 7%	1903
	21st to end	Day	44% 2 8% 22% 15% 9%	1650
March	1st to 10th	Day	58% 3 4 12% 16% 6%	4595
	11th to 20th	Day	44% 2 9% 28% 15% 3	5000
	21st to end	Day	55% 4 11% 18% 10% 1	5743
April	1st to 10th	Day	44% 4 12% 21% 17% 2	2400
	11th to 20th	Day	36% 5% 12% 23% 18% 6%	2372
	21st to end	Day	30% 4 13% 28% 21% 4	2400
May	1st to 10th	Day	20% 2 9% 26% 29% 14%	5650
	11th to 20th	Day	19% 2 9% 28% 35% 7%	6280
	21st to end	Day	14% 3 6% 32% 38% 6%	6904
June	1st to 10th	Day	24% 5% 10% 23% 29% 9%	2800
	11th to 20th	Day	12% 3 7% 21% 36% 20%	2800
	21st to end	Day	10% 1 3 16% 39% 32%	2800
July	1st to 10th	Day	3 1 1 6% 21% 68%	6251
	11th to 20th	Day	6% 1 1 5% 14% 72%	6245
	21st to end	Day	10% 1 2 16% 30% 42%	6374
August	1st to 10th	Day	13% 1 1 8% 25% 52%	4206
	11th to 20th	Day	5% 1 2 7% 43% 43%	3919
	21st to end	Day	8% 1 1 11% 45% 35%	4311
September	1st to 10th	Day	8% 1 2 11% 33% 45%	2400
	11th to 20th	Day	16% 3 4 21% 38% 19%	2400
	21st to end	Day	15% 2 5% 18% 35% 25%	2170
October	1st to 10th	Day	17% 2 3 12% 33% 33%	3280
	11th to 20th	Day	20% 2 4 18% 40% 17%	3261
	21st to end	Day	27% 1 5% 23% 30% 14%	3558
November	1st to 10th	Day	34% 3 8% 19% 22% 13%	1855
	11th to 20th	Day	37% 3 10% 18% 22% 10%	1890
	21st to end	Day	34% 3 6% 19% 23% 14%	1749
December	1st to 10th	Day	28% 2 7% 21% 26% 16%	2700
	11th to 20th	Day	54% 2 7% 15% 14% 8%	3084
	21st to end	Day	51% 3 11% 18% 13% 4	4004
January	1st to 10th	Night	41% 4 12% 20% 16% 7%	6306
	11th to 20th	Night	36% 3 7% 11% 26% 17%	6083
	21st to end	Night	43% 3 5% 11% 16% 23%	6468
February	1st to 10th	Night	42% 3 6% 18% 20% 12%	2600
	11th to 20th	Night	42% 4 7% 19% 20% 8%	2393
	21st to end	Night	42% 3 7% 21% 19% 8%	1980
March	1st to 10th	Night	54% 3 6% 16% 13% 7%	5296
	11th to 20th	Night	45% 2 7% 22% 20% 4	5000
	21st to end	Night	54% 5% 10% 18% 10% 2	5231
April	1st to 10th	Night	40% 4 13% 22% 17% 4	2000
	11th to 20th	Night	35% 4 13% 22% 19% 7%	1979
	21st to end	Night	28% 4 13% 32% 20% 3	2000
May	1st to 10th	Night	19% 5% 9% 26% 30% 10%	4334
	11th to 20th	Night	18% 3 8% 28% 31% 13%	3616
	21st to end	Night	13% 4 8% 30% 36% 9%	3972
June	1st to 10th	Night	21% 7% 10% 25% 26% 11%	1600
	11th to 20th	Night	11% 3 7% 22% 34% 23%	1600
	21st to end	Night	12% 1 4 14% 35% 35%	1600
July	1st to 10th	Night	3 1 1 6% 21% 68%	3600
	11th to 20th	Night	9% 1 1 5% 15% 70%	3592
	21st to end	Night	12% 1 2 13% 26% 45%	4164
August	1st to 10th	Night	15% 1 2 7% 24% 51%	2929
	11th to 20th	Night	5% 1 2 8% 39% 45%	3213
	21st to end	Night	9% 1 2 12% 36% 40%	3608
September	1st to 10th	Night	8% 1 3 9% 31% 48%	2000
	11th to 20th	Night	14% 2 5% 20% 38% 21%	2000
	21st to end	Night	13% 3 4 19% 33% 27%	2225
October	1st to 10th	Night	17% 2 3 11% 28% 40%	3920
	11th to 20th	Night	15% 1 4 24% 38% 18%	3897
	21st to end	Night	25% 2 4 22% 30% 17%	4253
November	1st to 10th	Night	33% 4 7% 21% 20% 16%	2663
	11th to 20th	Night	32% 4 10% 20% 22% 11%	2730
	21st to end	Night	33% 3 6% 20% 23% 15%	2867
December	1st to 10th	Night	26% 3 5% 20% 23% 22%	4700
	11th to 20th	Night	53% 2 5% 12% 20% 7%	5274
	21st to end	Night	57% 3 7% 16% 11% 6%	6952

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	43% 13% 20% 17% 7% 1	200
	11th to 20th	Day	30% 13% 25% 22% 9% 1	300
	21st to end	Day	29% 15% 21% 23% 10% 2	440
February	1st to 10th	Day	33% 16% 27% 17% 7% 1	400
	11th to 20th	Day	32% 19% 30% 15% 4	467
	21st to end	Day	28% 17% 34% 16% 5%	414
March	1st to 10th	Day	39% 23% 21% 13% 4 1	500
	11th to 20th	Day	35% 17% 24% 14% 8% 2	500
	21st to end	Day	34% 22% 27% 14% 3 1	550
April	1st to 10th	Day	25% 23% 30% 16% 5% 1	500
	11th to 20th	Day	28% 20% 30% 16% 5% 1	492
	21st to end	Day	18% 20% 31% 22% 8% 1	500
May	1st to 10th	Day	18% 26% 29% 18% 6% 2	503
	11th to 20th	Day	21% 19% 30% 20% 8% 4	528
	21st to end	Day	15% 15% 31% 25% 10% 4	573
June	1st to 10th	Day	10% 16% 32% 26% 10% 5%	530
	11th to 20th	Day	11% 18% 39% 19% 10% 4	530
	21st to end	Day	4 14% 39% 27% 10% 6%	530
July	1st to 10th	Day	3 10% 45% 26% 12% 4	526
	11th to 20th	Day	1 7% 44% 29% 12% 6%	524
	21st to end	Day	1 8% 42% 29% 13% 6%	575
August	1st to 10th	Day	4 9% 39% 32% 12% 4	527
	11th to 20th	Day	3 10% 38% 32% 12% 4	517
	21st to end	Day	3 9% 41% 34% 12% 2	583
September	1st to 10th	Day	3 12% 44% 28% 12% 1	530
	11th to 20th	Day	9% 12% 36% 31% 9% 2	530
	21st to end	Day	7% 14% 38% 31% 8% 1	530
October	1st to 10th	Day	9% 18% 32% 28% 11% 2	530
	11th to 20th	Day	12% 13% 30% 31% 11% 3	530
	21st to end	Day	15% 15% 27% 30% 10% 3	583
November	1st to 10th	Day	21% 11% 23% 26% 16% 3	331
	11th to 20th	Day	21% 12% 25% 25% 14% 3	330
	21st to end	Day	22% 13% 20% 27% 15% 3	256
December	1st to 10th	Day	23% 12% 23% 21% 15% 6%	220
	11th to 20th	Day	28% 13% 20% 23% 14% 2	214
	21st to end	Day	30% 15% 22% 20% 11% 1	220
January	1st to 10th	Night	28% 9% 25% 22% 12% 4	800
	11th to 20th	Night	22% 13% 27% 27% 10% 1	800
	21st to end	Night	25% 11% 23% 23% 15% 2	880
February	1st to 10th	Night	26% 12% 26% 25% 11% 1	800
	11th to 20th	Night	24% 11% 22% 26% 14% 3	784
	21st to end	Night	24% 12% 25% 28% 8% 2	660
March	1st to 10th	Night	31% 11% 21% 24% 12% 2	800
	11th to 20th	Night	28% 9% 19% 24% 19% 2	800
	21st to end	Night	29% 9% 23% 26% 12% 1	880
April	1st to 10th	Night	22% 8% 23% 32% 15% 2	800
	11th to 20th	Night	18% 11% 23% 31% 14% 3	791
	21st to end	Night	14% 8% 22% 34% 19% 4	800
May	1st to 10th	Night	12% 13% 22% 30% 20% 3	707
	11th to 20th	Night	10% 6% 19% 38% 22% 4	394
	21st to end	Night	12% 4 17% 35% 27% 6%	433
June	1st to 10th	Night	9% 4 16% 39% 29% 4	400
	11th to 20th	Night	4 6% 19% 39% 31% 3	400
	21st to end	Night	3 2 17% 44% 31% 4	400
July	1st to 10th	Night	1 1 16% 37% 41% 4	390
	11th to 20th	Night	1 1 13% 45% 35% 5%	388
	21st to end	Night	2 1 12% 34% 43% 8%	575
August	1st to 10th	Night	3 2 14% 41% 34% 6%	597
	11th to 20th	Night	2 2 16% 40% 34% 7%	761
	21st to end	Night	2 1 12% 47% 33% 5%	880
September	1st to 10th	Night	2 1 16% 43% 33% 5%	800
	11th to 20th	Night	4 2 16% 40% 29% 9%	800
	21st to end	Night	5% 5% 24% 36% 23% 8%	800
October	1st to 10th	Night	8% 7% 20% 39% 23% 4	800
	11th to 20th	Night	10% 7% 21% 34% 23% 5%	800
	21st to end	Night	12% 9% 23% 30% 21% 6%	880
November	1st to 10th	Night	18% 7% 18% 32% 20% 4	820
	11th to 20th	Night	16% 10% 25% 32% 15% 3	840
	21st to end	Night	17% 9% 29% 27% 16% 3	840
December	1st to 10th	Night	22% 13% 24% 28% 11% 2	840
	11th to 20th	Night	29% 9% 23% 27% 10% 2	828
	21st to end	Night	30% 14% 23% 24% 9%	880

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